1. Field of the Invention
The present invention relates to an image forming apparatus, a method of controlling the same, and a non-transitory computer-readable medium, and more particularly, to a technique for predicting, from an image signal, the amount of developing material to be consumed when printing an image by using a developing material based on the image signal.
2. Description of the Related Art
In general, for electrophotographic and electrostatic recording image forming apparatuses, properly supplying a developing material is a function necessary to maintain good image output. Color image forming apparatuses often use a developing material constituted by two components (two-component developing material) containing a magnetic powder called carrier particles in addition to toner particles as a coloring material in consideration of color reproducibility. For an image forming apparatus using a two-component developing material, the toner density of the developing material (that is, the ratio of a toner particle weight to the total weight of carrier and toner particles) is a very important factor for the stabilization of image quality. Since toner particles of a two-component developing material are consumed at the time of developing, the toner density changes. For this reason, it is necessary to control the toner density to always keep it constant so as to hold the quality of images by supplying toner in accordance with a change in toner density.
Conventional density controllers for controlling toner density include, for example, one that detects the density of developed toner by using various types of sensors. On the other hand, there has been developed a unit for calculating the amount of toner without using various types of sensors. A density controller based on a so-called video count method has been proposed as a controller used in a digital image forming apparatus, in particular. This method is configured to keep the toner density in a developing device constant by calculating a video count from an input multilevel image signal and deciding a toner supply amount upon predicting a toner consumption amount from the video count.
A problem of this technique is, however, that it requires a multivalued image signal and hence cannot cope with a case in which a halftone image signal representing the dot distribution of toner particles on a paper medium is directly supplied to an image forming apparatus.
In order to solve the above problem, there has been proposed a technique of predicting a toner consumption amount from a halftone image signal. For example, Japanese Patent Laid-Open No. 9-22226 discloses a technique of calculating the amount of toner consumed by counting the output signals of a halftone image and obtaining the product of the accumulated count value and the adhesion amount of toner per dot. In addition, Japanese Patent Laid-Open No. 2002-189385 discloses a technique of detecting a continuous dot count from a continuous output signal count and calculating a toner consumption amount after a series of dot formation based on data associating continuous dot counts with the representative values of toner consumption amounts.
The problem of incapability of coping with a change in the output density characteristics of an engine arises in the method of calculating a toner consumption amount, upon weighting a dot count value, such as the adhesion amount of toner per dot or the representative value for the continuous dot count as in the above technique. Assume that the output density characteristics of an image forming apparatus deteriorate due to an environmental change or temporal change. In this case, even if the apparatus receives halftone image signals with the same pattern, the density characteristics of printed products to be output deteriorate. This indicates that the toner consumption amount has decreased and the adhesion amount of toner per dot or the representative value for the continuous dot count change.